1. Technical Field
This invention relates generally to fluid handling and, more particularly, to vortex generators.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Various aerodynamic and hydrodynamic applications, including aeronautical, marine, and other applications, involve relative fluid flow across a surface. Examples include fluid flows over an aircraft wing or engine inlet, a watercraft hull or rudder, a wind turbine blade, and the like. During relative motion between a viscous fluid and a surface of a body across which the fluid flows, layers of fluid flow can be identified. Of those, the fluid flow layer closest to the body surface is known as the boundary layer.
The boundary layer is characterized by fluid laminae that decrease in fluid velocity relative to the body surface as a function of proximity to the surface. The flow in the boundary layer may be laminar wherein fluid laminae of different velocities create a smoothly-varying velocity profile to follow the contour of the surface. Downstream, however, the fluid flow in the boundary layer becomes turbulent wherein additional time dependent velocity perturbations occur in the fluid, creating additional mixing, however the mean flow continues to follow the contour of the surface. This turbulent boundary layer has higher mean velocities near the surface due to the additional mixing and is less susceptible to separation than a laminar boundary layer. In geometry regions where the surface turns too rapidly, or shock waves occur, the fluid flow may separate from the body surface, resulting in relatively low pressure and reversed flow near the body surface, thereby contributing to increased drag, a reduction in lift, or reduced control effectiveness.
Accordingly, vortex generators are used on body surfaces to delay and/or reduce flow separation and thereby reduce drag, increase lift, and/or increase control effectiveness. Vortex generators may include fins that extend from a body surface into higher velocity fluid flow and create tip vortices that draw higher velocity fluid toward the body surface through lower velocity fluid flow regions to energize the boundary layer and thereby promote flow attachment to the body surface. Vortex generators are particularly well suited to maintain attached flow across body surfaces disposed at large angles-of-attack to the relative wind, or across body surfaces with steep slopes, like a deflected flap or aileron or in an inlet duct to an engine. Conventional vortex generators are effective devices but their quantity and size can create counterproductive parasitic drag at off-design operating conditions.